The present invention relates to influenza virus vaccine compositions and methods of treating or preventing influenza infection and disease in mammals. Influenza is an acute febrile illness caused by infection of the respiratory tract. There are three types of influenza viruses: A, B, and C “IAV,” “IBV” or “IAC,” respectively, or generally “IV”. Type A, which includes several subtypes, causes widespread epidemics and global pandemics such as those that occurred in 1918, 1957 and 1968. Type B causes regional epidemics. Type C causes sporadic cases and minor, local outbreaks. These virus types are distinguished in part on the basis of differences in two structural proteins, the nucleoprotein, found in the center of the virus, and the matrix protein, which foams the viral shell.
The disease can cause significant systemic symptoms, severe illness requiring hospitalization (such as viral pneumonia), and complications such as secondary bacterial pneumonia. More than 20 million people died during the pandemic flu season of 1918/1919, the largest pandemic of the 20th century. Recent epidemics in the United States are believed to have resulted in greater than 10,000 (up to 40,000) excess deaths per year and 5,000-10,000 deaths per year in non-epidemic years.
The best strategy for prevention of morbidity and mortality associated with influenza is vaccination. Vaccination is especially recommended for people in high-risk groups, such as residents of nursing or residential homes, as well as for diabetes, chronic renal failure, or chronic respiratory conditions.
Traditional methods of producing influenza vaccines involve growth of an isolated strain in embryonated hens' eggs. Initially, the virus is recovered from a throat swab or similar source and isolated in eggs. The initial isolation in egg is difficult, but the virus adapts to its egg host and subsequent propagation in eggs takes place relatively easily. It is widely recognized, however, that the egg-derived production of IV for vaccine purposes has several disadvantages. One disadvantage is that such production process is rather vulnerable due to the varying (micro)biological quality of the eggs. Another disadvantage is that the process completely lacks flexibility if demand suddenly increases, i.e., in case of a serious epidemic or pandemic, because of the logistical problems due to the non-availability of large quantities of suitable eggs. Also, vaccines thus produced are contra-indicated for persons with a known hypersensitivity to chicken and/or egg proteins.
The influenza vaccines currently in use are designated whole virus (WV) vaccine or subvirion (SV) (also called “split” or “purified surface antigen”). The WV vaccine contains intact, inactivated virus, whereas the SV vaccine contains purified virus disrupted with detergents that solubilize the lipid-containing viral envelope, followed by chemical inactivation of residual virus. Attenuated viral vaccines against influenza are also in development. A discussion of methods of preparing conventional vaccine may be found in Wright, P. F. & Webster, R. G., FIELDS VIROLOGY, 4d Ed. (Knipe, D. M. et al. Ed.), 1464-65 (2001), for example.
Virus Structures
An IV is roughly spherical, but it can also be elongated or irregularly shaped. Inside the virus, eight segments of single-stranded RNA contain the genetic instructions for making the virus. The most striking feature of the virus is a layer of spikes projecting outward over its surface. There are two different types of spikes: one is composed of the molecule hemagglutinin (HA), the other of neuraminidase (NA). The HA molecule allows the virus to “stick” to a cell, initiating infection. The NA molecule allows newly formed viruses to exit their host cell without sticking to the cell surface or to each other. The viral capsid is comprised of viral ribonucleic acid and several so called “internal” proteins (polymerases (PB1, PB2, and PA, matrix protein (M1) and nucleoprotein (NP)). Because antibodies against HA and NA have traditionally proved the most effective in fighting infection, much research has focused on the structure, function, and genetic variation of those molecules. Researchers are also interested in a two non-structural proteins M2 and NS1; both molecules play important roles in viral infection.
Type A subtypes are described by a nomenclature system that includes the geographic site of discovery, a lab identification number, the year of discovery, and in parentheses the type of HA and NA it possesses, for example, A/Hong Kong/156/97 (H5N1). If the virus infects non-humans, the host species is included before the geographical site, as in A/Chicken/Hong Kong/G9/97 (H9N2).
Virions contain 7 segments (influenza C virus) to 8 segments (influenza A and B virus) of linear negative-sense single stranded RNA. Most of the segments of the virus genome code for a single protein. For many influenza viruses, the whole genome is now known. Genetic reassortment of the virus results from intermixing of the parental gene segments in the progeny of the viruses when a cell is co-infected by two different viruses of a given type. This phenomenon is facilitated by the segmental nature of the genome of influenza virus. Genetic reassortment is manifested as sudden changes in the viral surface antigens.
Antigenic changes in HA and NA allow the influenza virus to have tremendous variability. Antigenic drift is the term used to indicate minor antigenic variations in HA and NA of the influenza virus from the original parent virus, while major changes in HA and NA which make the new virions significantly different, are called Antigenic shift. The difference between the two phenomena is a matter of degree.
Antigenic drift (minor changes) occurs due to accumulation of point mutations in the gene which results in changes in the amino acids in the proteins. Changes which are extreme, and drastic (too drastic to be explained by mutation alone) result in antigenic shift of the virus. The segmented genomes of the influenza viruses reassort readily in double infected cells. Genetic reassortment between human and non-human influenza virus has been suggested as a mechanism for antigenic shift. Influenza is a zoonotic disease, and an important pathogen in a number of animal species, including swine, horses, and birds, both wild and domestic. Influenza viruses are transferred to humans from other species.
Because of antigenic shift and antigenic drift, immunity to an IV carrying a particular HA and/or NA protein does not necessarily confer protective immunity against IV strains carrying variant, or different HA and/or NA proteins. Because antibodies against HA and NA have traditionally proved the most effective in fighting IV infection, much research has focused on the structure, function and genetic variation of those molecules.
Recent IV Vaccine Candidates
During the past few years, there has been substantial interest in testing DNA-based vaccines for a number of infectious diseases where the need for a vaccine, or an improved vaccine, exists. Several well-recognized advantages of DNA-based vaccines include the speed, ease and cost of manufacture, the versatility of developing and testing multivalent vaccines, the finding that DNA vaccines can produce a robust cellular response in a wide variety of animal models as well as in humans, and the proven safety of using plasmid DNA as a delivery vector (Donnelly, J. J., et al., Annu. Rev. Immunol. 15:617-648 (1997); Manickan, E., et al., Crit. Rev. Immunol. 17(2):139-154 (1997); U.S. Pat. No. 6,214,804). DNA vaccines represent the next generation in the development of vaccines (Nossal, G., Nat. Med. 4(5 Supple):475-476 (1998)) and numerous DNA vaccines are in clinical trials. The above references are herein incorporated by reference in their entireties.
Studies have already been performed using DNA-based vaccines in animals. Ulmer, J. B. et al., Science 259:1745-9 (1993) revealed that mice could be protected by an IV nucleoprotein DNA vaccine alone against severe disease and death resulting from either a homologous or a heterologous IV challenge. Further studies have substantiated this model, and comparative studies of live influenza vaccines versus DNA influenza vaccines show them to be relatively equivalent in immune induction and protection in the murine model.
WO 94/21797, incorporated herein by reference in its entirety, discloses IV vaccine compositions comprising DNA constructs encoding NP, HA, M1, PB1 and NS1. WO 94/21797 also discloses methods of protecting against IV infection comprising immunization with a prophylactically effective amount of these DNA vaccine compositions.
The IV nucleoprotein is relatively conserved (see Shu, L. L. et al., J. Virol. 67:2723-9 (1993)), but just as conserved are the M1 matrix protein (which is a major T-cell target), and the M2 protein, which are encoded by separate reading frames of RNA segment 7. See Neirynck, S. et al., Nat. Med. 5:1157-63 (1999); Lamb, R. A. & Lai, C. J., Virology 112:746-51 (1981); Ito, T. et al., J. Virol. 65:5491-8 (1991). Animal DNA vaccine trials have been performed with DNA constructs encoding these genes alone or in combination, usually with success. See Okuda, K., et al., Vaccine 19:3681-91 (2001); Watabe, S. et al., Vaccine 19:4434-44 (2001). Of interest, the M2 protein is involved as part of an ion channel, is critical in resistance to the antiviral agents amantadine and rimantidine, and approximately 24 amino acids are extracellular (eM2). See Fischer, W. B., Biochim Biophys Acta 1561:27-45 (2002); Zhong, Q., FEBS Lett 434:265-71 (1998). Antibodies to this extracellular, highly conserved protein (eM2), which is highly expressed in infected cells (Lamb, R. A., et al., Cell 40:627-33 (1985)), have been shown to be involved in animal models. Treanor, J. J., J. Virol. 64:1375-7 (1990); Slepushkin, V. A. et al., Vaccine 13:1399-402 (1995). An approach using a conjugate hepatitis B core-eM2 protein has been evaluated in an animal model and proposed as a pandemic influenza vaccine. Neirynck, S. et al., Nat. Med. 5:1157-63 (1999). However, in one study vaccination of pigs with a DNA construct expressing eM2-NP fusion protein exacerbated disease after challenge with influenza A virus. Heinen, P. P., J. Gen. Virol. 83:1851-59 (2002). All of the above references are herein incorporated by reference in their entireties.
Heterologous “prime boost” strategies have been effective for enhancing immune responses and protection against numerous pathogens. Schneider et al., Immunol. Rev. 170:29-38 (1999); Robinson, H. L., Nat. Rev. Immunol. 2:239-50 (2002); Gonzalo, R. M. et al., Vaccine 20:1226-31 (2002); Tanghe, A., Infect. Immun. 69:3041-7 (2001). Providing antigen in different forms in the prime and the boost injections appears to maximize the immune response to the antigen. DNA vaccine priming followed by boosting with protein in adjuvant or by viral vector delivery of DNA encoding antigen appears to be the most effective way of improving antigen specific antibody and CD4+ T-cell responses or CD8+ T-cell responses respectively. Shiver J. W. et al., Nature 415: 331-5 (2002); Gilbert, S. C. et al., Vaccine 20:1039-45 (2002); Billaut-Mulot, O. et al., Vaccine 19:95-102 (2000); Sin, J. I. et al., DNA Cell Biol. 18:771-9 (1999). Recent data from monkey vaccination studies suggests that adding CRL1005 poloxamer (12 kDa, 5% POE), to DNA encoding the HIV gag antigen enhances T-cell responses when monkeys are vaccinated with an HIV gag DNA prime followed by a boost with an adenoviral vector expressing HIV gag (Ad5-gag). The cellular immune responses for a DNA/poloxamer prime followed by an Ad5-gag boost were greater than the responses induced with a DNA (without poloxamer) prime followed by Ad5-gag boost or for Ad5-gag only. Shiver, J. W. et al. Nature 415:331-5 (2002). U.S. Patent Appl. Publication No. US 2002/0165172 A1 describes simultaneous administration of a vector construct encoding an immunogenic portion of an antigen and a protein comprising the immunogenic portion of an antigen such that an immune response is generated. The document is limited to hepatitis B antigens and HIV antigens. Moreover, U.S. Pat. No. 6,500,432 is directed to methods of enhancing an immune response of nucleic acid vaccination by simultaneous administration of a polynucleotide and polypeptide of interest. According to the patent, simultaneous administration means administration of the polynucleotide and the polypeptide during the same immune response, preferably within 0-10 or 3-7 days of each other. The antigens contemplated by the patent include, among others, those of Hepatitis (all forms), HSV, HIV, CMV, EBV, RSV, VZV, HPV, polio, influenza, parasites (e.g., from the genus Plasmodium), and pathogenic bacteria (including but not limited to M. tuberculosis, M. leprae, Chlamydia, Shigella, B. burgdorferi, enterotoxigenic E. coli, S. typhosa, H. pylori, V. cholerae, B. pertussis, etc.). All of the above references are herein incorporated by reference in their entireties.